In a compact disc player which carries a compact disc through a carrying roller to a support plate for playing, a trigger device is usually adopted to detect whether the center of the compact arrives the center of the support plate, and actuates a clamp mechanism of the compact disc. One end of the trigger device is given a rotation force pointing to the direction of the compact disc entry under the effect of a spring, and contacts the outer circumference of the compact disc carried in the carrying path, the other end of the trigger device is pushed and rotates under the acting force against the spring, so as to actuate the clamp mechanism finally. The spring of the trigger device mentioned above may function to block the carrying of the compact disc. After the carrying roller is disengaged from the compact disc, the trigger device may return the compact disc carried on the support plate in the direction of the compact disc entry. In this way, there may be an offset between the position of the center of the compact disc and that of the support plate, so that the action of the clamp can not be performed accurately. On the other hand, after the center of the compact disc exceeds the center of the support plate by one millimeter, the outer circumference of the compact disc is in contact with the baffle on the base plate, and accordingly the carrying roller stops the carrying of the compact disc. Then, the clamp mechanism is actuated under this condition and performs the clamp action. Therefore, the clamp has been always operated in the case that the position of the center of the compact disc is inconsistent with that of the support plate.
As a method to solve the problem, a solution is proposed in Japanese Patent Application Laid-Open No. 2006-48837. In this solution, a second centering mechanism 2 is disposed between the support plate and the carrying roller, and a positioning mechanism 3 is disposed in the rear portion of the support plate. Under the combination effect of the second centering mechanism and the compact disc positioning mechanism, the whole circumference of the compact disc carried to the support plate is clamped, thereby keeping the center of the compact disc on the center position of the support plate. The addition of a plurality of parts is required in this solution, which makes the structure complicated.